The answer is SocketCAN, a set of open source CAN drivers and a networking stack contributed by Volkswagen Research to the Linux kernel. We can connect 3 wires from the car, GND, MSCANH, MSCANL to a Kvaser Leaf Light HSv2 ($300 on Amazon) or to a CANable ($25 on Tindie) and get a computer with a recent Linux kernel to load the CAN bus as a network device. A CAN bus monitor is an analysis tool, often a combination of hardware and software, used during development of hardware making use of the CAN bus. Typically the CAN bus monitor will listen to the traffic on the CAN bus in order to display it in a user interface.